What is the surface of a comet like? That's one of the main questions that motivated Philae's mission to the surface of comet 67P/Churyumov-Gerasimenko. We now know the comet has a rigid crust about 10 to 50 centimeters thick, below which the comet is much more fluffy.

Opportunity spent April further exploring the area about halfway down Perseverance Valley, checking out unusual, vesicular or pitted rocks the likes of which she has never seen, while officials prepared the mission’s bid to keep the robot field geologist roving through 2019.

MarCO or Mars Cube One is an experimental mission that is sending two tiny spacecraft along with InSight to Mars. If successful, they will relay real-time telemetry from InSight to Earth during the landing.